Assert endpoints basePath starts with '/' or is empty

Fixes gh-12489

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/endpoint/web/WebEndpointProperties.java

@@ -22,6 +22,7 @@ import java.util.Map;
 import java.util.Set;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
 /**
@@ -56,6 +57,8 @@ public class WebEndpointProperties {
 	}
 
 	public void setBasePath(String basePath) {
+		Assert.isTrue(basePath.isEmpty() || basePath.startsWith("/"),
+				"Base path must start with '/' or be empty");
 		this.basePath = cleanBasePath(basePath);
 	}
 

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/endpoint/web/WebEndpointPropertiesTests.java

@@ -16,7 +16,9 @@
 
 package org.springframework.boot.actuate.autoconfigure.endpoint.web;
 
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.ExpectedException;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -27,6 +29,9 @@ import static org.assertj.core.api.Assertions.assertThat;
  */
 public class WebEndpointPropertiesTests {
 
+	@Rule
+	public ExpectedException thrown = ExpectedException.none();
+
 	@Test
 	public void defaultBasePathShouldBeApplication() {
 		WebEndpointProperties properties = new WebEndpointProperties();
@@ -38,6 +43,23 @@ public class WebEndpointPropertiesTests {
 		WebEndpointProperties properties = new WebEndpointProperties();
 		properties.setBasePath("/");
 		assertThat(properties.getBasePath()).isEqualTo("");
+		properties.setBasePath("/actuator/");
+		assertThat(properties.getBasePath()).isEqualTo("/actuator");
+	}
+
+	@Test
+	public void basePathMustStartWithSlash() {
+		WebEndpointProperties properties = new WebEndpointProperties();
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("Base path must start with '/' or be empty");
+		properties.setBasePath("admin");
+	}
+
+	@Test
+	public void basePathCanBeEmpty() {
+		WebEndpointProperties properties = new WebEndpointProperties();
+		properties.setBasePath("");
+		assertThat(properties.getBasePath()).isEqualTo("");
 	}
 
 }